Power transistor packages typically include a conductive flange on which an insulative window is arranged. A power transistor is mounted to the flange within the window so that the source of the power transistor can be directly connected to the flange and grounded. Input and output terminals are attached to the insulative window so that input (gate) and output (drain) connections, respectively, can be made to the power transistor. The drain of the power transistor must be sufficiently DC biased to ensure proper operation. A DC feed path is typically provided in the form of one or more DC feed terminals each of which is attached to the insulative window so that the drain of the power transistor can be biased. For example, one DC feed terminal may be spaced apart from and extend along one side of the output terminal while another DC feed terminal is spaced apart from and extends along the other side of the output terminal as disclosed in U.S. Pat. No. 6,734,728, the contents of which are incorporated herein by reference in their entirety.
The end of each DC feed terminal is typically wire bonded to an output matching blocking capacitor coupled via a matching inductance to the drain of the power transistor. The output matching inductance is provided an RF ground by this capacitor. The juncture of this inductance and capacitance create an RF “cold” point that may be used to apply DC and/or decouple and terminate low frequencies. The end of the DC feed terminal which terminates adjacent the output capacitor has limited area for connecting the DC feed terminal to the matching capacitor. This limits the number of wire bond connections which can be made between the end of the DC feed terminal and the output capacitor. Accordingly, only a few bond wires are available for carrying the entire DC bias current to the drain of the power transistor. Power transistors having high operating currents cannot reliably employ conventional DC feed structures because only a few wire bonds connect the DC feed terminal to the output capacitor, thereby limiting the low frequency current carrying capability of the package.
In addition, the wire bonds typically extend from the end of each DC feed terminal to respective ends of the output capacitor. This node of the capacitor is also wire bonded to the drain of the power transistor and the other capacitor node is grounded. However, feeding DC power only to the ends of the output capacitor induces an IR drop between the ends and center region of the capacitor node. Accordingly, the center of the capacitor node is not at the same low frequency potential as the ends of the node during operation of the power transistor. This IR drop propagates to the drain of the power transistor, creating unbalanced low frequency termination points across the drain. This causes some regions of the drain (e.g., the end regions) to be biased differently than other regions of the drain (e.g., the center region), causing unintentional LC filtering which degrades power transistor performance. The IR drop across the capacitor node worsens as a function of capacitor length, limiting the length of the capacitor and thus the number of power transistors which can be included in the package.